1. Field of the Invention
This invention relates generally to waveguides, and more specifically to a method of forming a single-mode polymer waveguide array connector.
2. Description of the Related Art
In the field of building of an optical interconnection system, a polymer waveguide is attracting attention. Compared with an approach involving arranging and fixing a plurality of fibers in an array, the polymer waveguide can provide a more inexpensive optical signal channel with higher reliability because an integrated polymer waveguide array can be formed in a process using the polymer material.
FIG. 1 is a perspective view for illustrating a configuration of a single-mode polymer waveguide array connector.
The waveguide array connector comprises a waveguide array and a plurality of ferrules attached to the opposite ends of the waveguide array. The ferrule is a main component of an optical connector that houses and holds an optical waveguide array or an optical fiber array. There are standards for the shape, size and other aspects of the ferrule, and the ferrule in this example complies with such a standard. However, for simplification of the description, the ferrule is only schematically shown in this drawing.
The waveguide array comprises a plurality of cores and a cladding surrounding the cores. Each of the plurality of cores can independently guide single-mode light entering from one connector to the other connector.
FIG. 2 is a perspective view for illustrating a state of interconnection of two single-mode polymer waveguide array connectors, or a single-mode polymer waveguide array connector and a single-mode fiber array connector.
The two single-mode polymer waveguide array connectors, or the single-mode polymer waveguide array connector and the single-mode fiber array connector, connected to each other are in close contact with each other. The ferrule is a component to house and hold the waveguide array or fiber array in the optical connector.
A plurality of single-mode polymer waveguide array connectors or fiber array connectors can be coupled to each other by such connection, thereby interconnecting optical signal transmission systems.
In a typical example, as illustrated in FIG. 2(A), guide pins are passed through guide pin holes in two ferrules, thereby fixing the ferrules connected to each other.
In this typical example, the center of the guide pin hole is an absolute reference position in connection of two ferrules. However, the method of fixing the ferrules is not limited to this approach. The absolute reference position may vary with the way of mechanical connection and therefore is not limited to, and may be different from, the position in this example.
The plurality of cores separately guides single-mode light. Therefore, in order to achieve efficient optical signal connection with two ferrules are connected to each other, the precision of positioning of the plurality of cores is important.
More specifically, referring to FIG. 2(B), it is important to reduce the offset of the position (x, y) of the center of each core with respect to the absolute reference position in the connecting surfaces (in a two-dimensional plane) of the plurality of cores, that is, errors δx and δy, to fall within an allowable range. (Note that typically y=0 in the case of a single-layered waveguide array.)
FIG. 3 is a graph showing relationships between the offset of the position of a core center with respect to the absolute reference position and the optical signal loss in the connection of connectors in the case of a polymer waveguide for Multi-Mode® light.
As known, the scale of the core (diameter) of the polymer waveguide for multi-mode light is much larger than the size of the core of the polymer waveguide for single-mode light.
However, the multi-mode light is described herein as an example for the purpose of qualitative description. As known, there is a tendency that the larger the offset of the position (“Offset” shown in μm (micron) on the horizontal axis of the graph), the higher the coupling loss (in dB (decibel) on the vertical axis of the graph) becomes.
A method of reading the coupling loss from this graph will be described. As can be seen from the plots being shown by different types of marks, the coupling loss also depends on the size (ranging from 0 μm to 50 μm) of the gap (in the direction perpendicular to the sheet of FIG. 2(B) showing the ferrule connecting surface (in a two-dimensional plane)) between the connecting surfaces of the plurality of ferrules to be connected.
As can be read from this graph, in an ideal state where the size of the gap is reduced to be close to 0 μm, the coupling loss can be reduced to be lower than 0.5 dB if the positioning error of the ferrule connecting surface (in a two-dimensional plane) is reduced to be smaller than 5 μm.
However, in case of handling single-mode light, as known, more strict positioning precision is required. Theoretically, in order to reduce the coupling loss to be equal to or lower than 0.5 dB as in the case of the multi-mode light, positioning has to be achieved with such an extremely high precision that the positioning error δx<0.5 μm to 1.0 μm and the positioning error δy<0.5 μm to 1.0 μm. Otherwise, the positioning error directly leads to a coupling loss.
In addition, as more ferrules are connected to elongate the optical signal channel, the coupling losses of the ferrules are accumulated.
JP2005-3875A relates to a method of manufacturing a connector-integrated polymer waveguide. With regard to the waveguide manufacturing process, the method that involves forming a core recess according to JP2005-3875A differs from the method according to the present invention in that it does not involves a process of using a plurality of molds.
Concerning the core positioning precision, JP2005-3875A describes that “fixed in a state where the center of the core of the optical waveguide and the center of the connector sleeve are generally on the same straight line” and mentions “using a mold”. However, unlike the present invention, there is no mention of an attempt to define the core positioning precision in association with a “ferrule”.
JP2005-3875A describes a required core size of a single-mode waveguide and a desired core positioning precision and therefore can be informative in understanding the strictness of the precision.
JP2004-93989A describes a method of manufacturing a waveguide die and a method of manufacturing a waveguide that involves forming a core recess by “pressing” a die with a projection against a cladding material (an embossing process).
The method according to JP2004-93989A significantly differs from the method according to the present invention in that it does not involve pressing from above and below with a plurality of molds (resin molds).
JP2004-361613A discloses a process of manufacturing a polymer waveguide that can be said to be substantially the same as the process according to JP2005-3875A.
JP2011-17933A discloses a technique for solving an object similar to the object of the present invention (to improve the positioning precision of a core of an optical waveguide), although it is useful only as a reference. The technique is to solve the object in a different approach than the present invention.
To begin with, there seems to be no optical waveguide array connector that is capable of handling single-mode light.